1. Field of the Invention
The present invention relates to a receiver for use in a mobile communication system of CDMA (Code Division Multiple Access) method, and more specifically to a CDMA receiver capable of selecting a transport format (Transport Format: hereinafter, referred to as TF) of high reliability when determining transport format information for use in the decoding processing of a transport channel.
2. Description of the Related Art
Heretofore, this kind of CDMA receiver has offered a communication service for transmitting and receiving data of different types in various combinations, in order to cope with the recent progress of multi-media communication. The data combination information of several differently-defined TFs in this communication service is basically shown by Transport Format Combination Indicator (hereinafter, referred to as TFCI). This TFCI is the value indicating the combination of the TF (Transport Format) information in each transport channel, which is embedded into a wireless frame separately from data or information signal.
Since a transmitting party transmits the combination as TFCI, a receiving party has to receive it correctly. When the receiving party receives the TFCI improperly, the TF concerned with the whole frame of the received data will be improperly recognized and the data of the whole frame cannot be received correctly.
In order to solve this problem, there is disclosed a device for improving the accuracy in receiving and decoding data in an interleave period by more correctly detecting the TFCI for use in the receiving processing of each frame when receiving the data of interleave length over one frame (for example, refer to Japanese Patent Publication (Kokai) No. 2003-037583 (FIG. 1 and FIG. 2)).
For example, as illustrated in FIG. 10, a data signal received by an antenna and decoded by a receiver 101 enters a data separator 105. The mark of the TFCI included in this signal is detected through demapping by a TFCI detector 102 and kept in a TFCI holding unit 103.
A TFCI selector 104 decides the TFCI of the current frame, for example, by the rule of majority, when the kept TFCIs include different types. The decided TFCI is transmitted to the data separator 105 and the data separator 105 separates the received data of the above frame simultaneously transmitted from the receiver 101 according to this TFCI.
With reference to FIG. 11, the case of receiving four frames of every 10 ms during the elapse time of 40 ms will be described. When the send TFCIs corresponding to the four frames are “2, 2, 2, 2”, the receive TFCIs should be “2, 2, 2, 2”.
As shown in a state of the wireless communication of propagating through the air, however, the TFCI “1” is detected in the period of 30 ms corresponding to the third frame.
Since the TFCIs “2” are detected in the first frame of 10 ms period and the second frame of 20 ms period, it makes an adjustment to modify the third TFCI to “2” by the rule of majority. Although the rule of majority is adopted as an adjustment method in this example, the above patent publication says that the receiving quality based on the receiving level may be adopted.
This kind of CDMA receiver generally requires the TF information including the block size and the number of blocks, that is the data unit used for the decoding processing, including transport channel separation, first interleaving, rate matching, error correction decoding by Viterbi decoder or turbo decoder, and CRC judgment (for example, refer to P. 103-119 and 143-146 of “W-CDMA Mobile Communication System” under the editorship of Keiji Tachikawa, published by Maruzen Co., Ltd. on Jun. 25, 2001).
This TF information is to be decided for every channel called a Transport Channel (hereinafter, abbreviated as transport CH) and it may take various values according to a cycle called as a Transmission Time Interval (hereinafter, abbreviated as TTI). This TTI takes the integral multiple value of the wireless frame length that is the minimum data unit of a wireless interface. As mentioned above, in a wireless period, since a plurality of transport CHs are multiplexed and then transmitted, the above TFCI indicating the combination of the TF information of each transport CH is embedded into a wireless frame and transmitted separately from the information signal.
Accordingly, before starting the decoding processing in the decoder of the CDMA receiver, it is necessary to judge the received TFCI signal and know the TF information necessary for the decoding processing of each transport CH. The TFCI can be changed in every minimum TTI in each transport CH and the TF information of the transport channel in which the TTI is not equal to the minimum transport time interval has to be constant within the interleaving, namely within the TTI.
The TFCI signal, mapped into one code of 30 bit length, is converted into the Reed-Muller code and transmitted.
The above-mentioned conventional CDMA receiver is provided with adjusting means for correcting an error of TFCI according to the rule of majority or the receiving quality, in order to correct the error of the combined transport formats. However, it is the transport format varying according to every transport channel that determines the size of the transport channel and the TFCI itself is changed in the minimum TTI of the multiplied transport channel. Therefore, the effective result on the error correction cannot be expected disadvantageously.
Namely, since it is impossible to judge whether the TFCI decoding algorithm has an error in the decoded TFCI, the system performs the decoding processing as if the obtained TFCI indicated the correct state of each transport channel of the wireless frame when the TFCI is decoded improperly.
Therefore, the multiplexing parameter, the rate matching, and the error correction decoding processing are improperly performed, which results in losing the wireless frame data of each transport channel. This failure is not detected until the following CRC (Cyclic Redundancy Check).
Since the upper layer function requires the system to transmit the lost wireless frame again, as a result of the loss of the information, a network will transmit the data again. Since the wireless resources are limited, however, the efficiency of using the wireless resources is deteriorated owing to the retransmission.